Many diseases alter the mechanical properties of a tissue. Accordingly, the mechanical properties can serve as biomarkers for disease, diagnosis and tumor assessment. While some larger diseased tissues or abnormalities near the surface of a patient can be detected by palpitation, many are located deep within the patient or too small to identify. Some indications include liver fibrosis or other growths inside the thoracic cavity. A non-invasive means for detecting mechanical properties of a patient would provide physicians with a reliable tool to diagnose and monitor diseased tissue.
Viscoelastic materials (also called complex fluids) exhibit the elastic properties of solids as well as the viscous flow characteristics of fluids in response to shearing stresses. The study of the mechanical properties of viscoelastic materials is known as ‘rheology.’ Rheo-NMR uses nuclear magnetic resonance (NMR) to measure the fluid flow response to deformational stresses.
Magnetic Resonance Elastography (MRE) is one non-invasive method for detecting mechanical properties in a tissue in the field of Rheo-NMR. MRE mechanically excites the tissue by introducing shear waves through ultrasound. Nuclear Magnetic Resonance Images (MRI) of the propagation of the shear waves are taken. Specific mathematical algorithms are used to interpret the images and generate quantitative images depicting tissue stiffness. The mechanical excitation drastically complicates the imaging process in terms of hardware design, imaging implementation and data analysis. MRE cannot be performed using a conventional medical MRI machine.